Method for detecting chemical substances

ABSTRACT

A method for detecting and identifying a chemical substance in various phases such as a vapor phase and a liquid phase. The chemical substance being measured is diffused into a predetermined phase. Then, an electric state at an electrode existing in the predetermined phase is detected as a change with time based on the diffusion and absorption of the chemical substance on the electrode. A pattern of the change of the electric state with time is prepared. A fitting function based on the pattern is set and parameters of the chemical substance being measured are found. A distance between the parameters of the chemical substance being measured and parameters of the reference substance which is detected is determined. In the case of a detection of a chemical substance in a liquid phase, before detecting the electric state at the electrode existing in the liquid phase, a predetermined electrolytic solution is supplied around the electrode to stabilize the electric state of the electrode and then the liquid phase containing the chemical substance being measured is supplied to the electrode.

RELATED APPLICATION

This is a continuation in part of application Ser. No. 08/551,865, filedNov. 21, 1995, now U.S. Pat. No. 5,545,299, which is a divisional ofapplication Ser. No. 08/305,157, filed Sep. 13, 1994, now U.S. Pat. No.5,496,451.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and a sensor for detecting chemicalsubstances contained in various phases, such as a vapor phase or aliquid phase.

2. Description of the Related Art

Hitherto, gas or liquid chromatography, etc., has been used to detectsubstances contained in a vapor or liquid phase, and various substanceconcentrations in a sampled gas or liquid are detected. However, thechromatography method basically requires that human beings samplespecimens. It is not suited for automatically detecting substances in avapor or liquid phase.

A vapor phase sensor is known which comprises a plurality of electrodes,whose electrical conditions (normally, potential and current dependingon oxidation-reduction potential change) change according to thesubstance concentration, etc., in a vapor phase. The electrodes areinstalled in a vapor phase and the electrical conditions of theelectrodes are detected for determining the substance amount in thevapor phase. Such a vapor phase sensor can be used to detect theconcentration of any desired gas simply by installing the sensor in thedetected atmosphere. The concentration of the gas to be measured canalso be measured by using films, membranes, etc., having gasselectivity.

Such vapor phase sensors are described in Japanese Patent Laid-Open Nos.Hei 5-10905, 5-60727, 5-45321, etc., for example.

However, in detecting chemical substances with such conventionalsensors, basically only a potential or current change is measured. Theconcentration of a single gas or a total potential or current change ofgases can only be measured by one sensor, and substances contained in avapor phase cannot be identified.

The freshness of various foods is often estimated from factors such asthe storage condition (freezing, cold storage) and the number of storagedays of the foods. On the other hand, very fresh beef is not necessarilygood while mature beef is preferred as food. In the final stage of thedistribution process, frozen beef is not simply thawed, but exposed to apredetermined temperature and humidity in a thawing and maturing chamberfor providing mature beef.

However, the degree of maturity varies depending on the condition of thefrozen beef before its freezing, etc. At this time, human beings inspectthe condition of thawed beef to determine the degree of maturity. Suchjudgment by human beings leads to inefficient work and moreover variesdepending on the individual. Therefore, it is desired to measure thedegree of maturity (freshness) easily and rapidly.

The measurement needs to be made while being out of contact with thefood to comply with food hygiene management laws, etc., and in such away that the food is not destroyed while being measured during qualitycontrol.

In the case of quality control of liquid materials such as mineralwater, (alcoholic) beverages or liquid seasonings, the judgment by humanbeings leads to inefficient work and moreover varies depending on theindividual. At this time, human beings inspect the condition of thesematerials--from factors such as color, taste or smell--to determine thedegree of freshness. Therefore, it is also desired to measure the degreeof quality (freshness) easily and rapidly for these liquid phasematerials.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a detection methodcapable of identifying chemical substances contained in a vapor phase.

It is another object of the invention to provide a vapor phase sensorcapable of specifying substances contained in a vapor phase.

It is a further object of the invention to provide a method of measuringthe freshness of foodstuffs, such as beef, efficiently in a non-contactand nondestructive manner.

To these ends, according to the invention, there is provided a method ofdetecting a chemical substance in a vapor phase comprising the steps ofholding an electrolytic solution, having a surface coming into directcontact with a vapor phase, around electrodes, diffusing a chemicalsubstance in the vapor phase into the electrolytic solution, anddetecting an electric state at the electrodes existing in theelectrolytic solution as a change with time based on the diffusion andabsorption of the chemical substance on the electrodes, wherein thechemical substance in the vapor phase is detected based on the detectedchange with time.

The step of holding the electrolytic solution around the electrodes iseffected by using surface tension thereof, and an electrolytic solutionis supplied from an electrolytic solution reservoir for holding the newelectrolytic solution, thereby repeating detection.

The chemical substance detection method according to the inventiondetects a change with time of the electric state caused by a chemicalsubstance in a vapor phase diffusing into a held electrolytic solution.The change with time varies depending on the chemical substance. Aspecific chemical substance can be identified according to the changepattern.

If the electrolytic solution is held using surface tension, theelectrolytic solution can be updated by supplying a new electrolyticsolution, thus an analysis on a new pattern and identification of achemical substance can be repeated.

According to the invention, there is provided a method of identifying achemical substance contained in a vapor phase comprising the steps of(A) holding an electrolytic solution, having a surface coming intodirect contact with a vapor phase, around electrodes; (B) obtaining apredetermined fitting function and parameters from a chemical substanceselected as a reference substance, by (b1) diffusing the chemicalsubstance selected as the reference substance into the electrolyticsolution, (b2) detecting an electric state at the electrodes existing inthe electrolytic solution as a change with time based on the diffusionand absorption of the chemical substance on the electrodes and preparinga pattern of change of the electric state with time, and (b3) setting afitting function based on the pattern and finding parameters of thereference substance for the fitting function; (C) obtainingpredetermined parameters from a chemical substance being measured, by(c1) diffusing the chemical substance being measured into theelectrolytic solution, and (c2) detecting an electric state at theelectrodes existing in the electrolytic solution as a change with timebased on the diffusion and absorption of the chemical substance on theelectrodes and preparing parameters of the substance being measured forthe fitting function; and (D) calculating a distance between theparameters of the reference substance and the parameters of thesubstance being measured and determining that the reference substancehaving the minimum distance therebetween is most similar to thesubstance being measured.

In the chemical substance identification method as described above, asimilarity between electric state change patterns with time isquantified and the degree of similarity between chemical substances isdetermined based on the quantified value. Specifically, the electricstate change patterns with time are compared with each other bycalculating the distance between the parameters for one pattern andthose for the other pattern for a fitting function. The similaritybetween the patterns is quantified as the distance between theparameters.

According to the chemical substance identification method according tothe invention, patterns of reference substances and substances beingmeasured (electric state change patterns with time) are prepared byusing the detection method of the invention mentioned above. A properfitting function is derived from the patterns of the different referencesubstances. At the same time, the parameters of the reference substancesare calculated for the fitting function. On the other hand, theparameters of the chemical substance being measured are also calculatedfor the fitting function. The distance between the parameters of thereference substances and the parameters of the substance being measuredis calculated. It is determined that the reference substance having theminimum distance therebetween is most similar to the substance beingmeasured. For example, it is determined that the measured substancehaving parameters close to the parameters of ethanol is a compoundsimilar to ethanol and that the substance having parameters far fromthose of ethanol is not similar to ethanol. Of course, if the substancehas the same parameters as ethanol, it is identified as ethanol. Thedistance between parameters can be calculated from n parameters. Forexample, a method such as a Euclidean distance, squared Euclideandistance, Chebychev distance, or 1-correlation coefficient calculationmethod can be used as the distance calculation method betweenparameters.

According to the invention, there is provided a vapor phase sensorcomprising measurement electrodes, a reference electrode, anelectrolytic solution holding surface comprising at least themeasurement electrodes and the reference electrode for holding anelectrolytic solution having an outer surface exposed directly to avapor phase on surfaces of the measurement electrodes and the referenceelectrode by using surface tension thereof, a source for supplying anelectrolytic solution onto the electrolytic solution holding surface,and a section for detecting an electric state change between themeasuring electrodes and the reference electrode caused by a chemicalsubstance in a vapor phase diffusing into the electrolytic solution,wherein the electrolytic solution held on the electrolytic solutionholding surface is updated by supplying an electrolytic solution fromthe electrolytic solution reservoir for detecting a substance in a vaporphase whenever necessary in the updated solution condition.

The vapor phase sensor may further include means for removing anelectrolytic solution held on the electrolytic solution holding surface.The removal means can be provided by combining a supply pipe forsupplying an electrolytic solution onto the electrolytic solutionholding surface and a discharge pipe for discharging the electrolyticsolution from the electrolytic solution holding surface.

Further, the surfaces of the measurement electrodes may be made ofconducting polymer films. The films made of conducting polymers can beformed with electrochemically polymerized films, for example.

A predetermined amount of an electrolytic solution is held on theelectrolytic solution holding surface by supplying the electrolyticsolution in the predetermined amount from the electrolytic solutionreservoir. Since the surface of the electrolytic solution is exposeddirectly to the air, chemical substances in a vapor phase are diffusedinto the electrolytic solution efficiently. Then, the chemicalsubstances can be detected stably based on a potential change betweenthe measurement electrodes and the reference electrode. Since theelectrolytic solution held on the electrolytic solution holding surfacecan be replaced by supplying another electrolytic solution, a change inthe atmosphere can also be handled easily and measurement can be madewhenever necessary.

If the electrolytic solution cannot easily be replaced due to oversupplyof electrolytic solution (for example, when the electrolytic solutionholding surface is facing upward) the removal means installed in thevapor phase sensor enables easy replacement of the electrolytic solutionfor updating the gas reception section.

Further, high-performance detection can be maintained over a long termby making the surface of measurement electrodes of conducting polymerfilms.

According to the invention, there is provided a method of measuringfreshness of foodstuffs comprising the steps of installing electrodes inan electrolytic solution into which chemical substances discharged intoa vapor phase from a foodstuff are diffused, and detecting an electricstate of the electrodes and measuring freshness of the foodstuff basedon a change in the electric state of the electrodes obtained.

The foodstuff may be beef. The films attached on the electrode surfacemay be made of conducting polymer films.

Thus, according to the invention, chemical substances contained in avapor or liquid phase discharged from food, beverage, water and liquidseasonings (such as odor substances), are diffused into an electrolyticsolution or absorbed on the electrodes, causing the electric state ofthe electrodes to change, and the freshness of food is measured inresponse to the electric state change of the electrodes. Thus,measurement can be made without intervention of human beings, andfreshness can be measured objectively. Particularly, it was difficult tomeasure freshness (maturity degree) of beef with conventional measuringinstruments, but the invention makes such a measurement possible.Preferably, the surface of the measurement electrodes are made ofconducting polymers.

It is another object of the invention to provide a detection methodcapable of identifying chemical substances contained in a liquid phase.

It is yet another object of the invention to provide a liquid phasesensor capable of specifying substances contained in a liquid phase.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing showing the configuration of a preferred vapor phasesensor of the invention;

FIG. 2 is a drawing showing the structure of a measurement section 10;

FIG. 3 is a flowchart showing the measurement operation of the vaporphase sensor of the invention;

FIG. 4 is a chart showing measurement patterns of substances;

FIG. 5 is a chart showing the relationship between dilution and responseamount;

FIG. 6 is a chart showing patterns of response to substances;

FIG. 7 is graphs showing the fitting results when parameters ofreference substances are assigned to a fitting function;

FIG. 8 is a drawing showing the contents of a database that storesparameters;

FIG. 9 is a chart showing a classification example of referencesubstances using cluster analysis;

FIG. 10 is a chart showing identification example 1 using clusteranalysis (example of identifying chemical substance A);

FIG. 11 is a chart showing identification example 2 using clusteranalysis (example of identifying chemical substance B);

FIG. 12 is a chart for illustrating update of a database by adding datato the database;

FIG. 13 is a chart showing response patterns which vary depending on thetype of films attached to the measurement electrode;

FIG. 14 is a graph showing response amounts for various substances;

FIG. 15 is a graph showing response amounts for various alcohols;

FIG. 16 is a graph showing the relationship between ethanolconcentration and response amount;

FIG. 17 is a drawing for illustrating preparation of anelectrochemically polymerized film;

FIGS. 18(a), 18(b), and 18(c) are drawings showing the structure of avapor phase sensor according to a second embodiment of the invention;

FIG. 19 is a flowchart showing the measurement operation of the vaporphase sensor according to the second embodiment of the invention;

FIG. 20 is a chart showing response patterns for beef of differentmaturity degrees;

FIG. 21 is a graph showing the relationship between the number ofstorage days and response amount; and

FIG. 22 is a block diagram showing the configuration of an odormeasuring system as one example of a measuring system of chemicalsubstances in a vapor phase.

FIG. 23 illustrates the configuration of a preferred liquid phase sensorin accordance with a third embodiment of the invention;

FIG. 24 illustrates the structure of a measurement section 210;

FIG. 25 is a flowchart showing the measurement operation of the liquidphase sensor in accordance with a third embodiment of the invention;

FIG. 26 is a block diagram showing the configuration of a measuringsystem of chemical substances in various liquid phases;

FIG. 27 illustrates the structure of a solution supply system forvarious liquid phases.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, there are shown preferredembodiments of the invention.

Configuration!

FIG. 1 is a drawing showing the overall configuration of a vapor phasesensor according to the first embodiment of the invention. FIG. 2 is anenlarged view showing the structure of a measurement section 10.

The measurement section 10 comprises two platinum electrodes 12 and 14and two fluorocarbon resin pipes 16 and 18 fixed with an epoxy resin 19,the lower face of which forms an electrolytic solution holding surface21. The films attached on first and second measurement electrodes 20 and22 made of different conducting polymers are formed on the lower facesof the platinum electrodes 12 and 14. That is, in the embodiment, thefirst measurement electrode 20 made of a PPy/PVS (polypyrrole doped withpolyvinyl sulfate ions) film is formed on the lower face of the platinumelectrode 12 and the second measurement electrode 22 made of a PPy/Cl(polypyrrole doped with chloride ions) film is formed on the lower faceof the platinum electrode 14. The platinum electrodes 12 and 14 may havethe lower ends only formed with platinum disks. The conducting polymerfilms are formed by electrochemical polymerization or chemicalpolymerization.

A salt bridge 29 made of 3M (mol/l) KCl (potassium chloride) and 3% agaris installed in the fluorocarbon resin pipe 16 and a silver-silverchloride electrode 24 is fitted to the opposite end of the salt bridge29, forming a reference electrode 26. Generally, the entire solutioncontaining the silver-silver chloride electrode 24 and chloride ions iscalled the reference electrode, but the lower end of the salt bridge 29is called the reference electrode 26 in the embodiment for thedescription of the operation, etc., because they are substantially thesame. On the other hand, the fluorocarbon resin pipe 18 is connected viaan electrolytic solution supply tube 18a to an electrolytic solutionsupply section 28 for supplying an electrolytic solution from the lowerend of the fluorocarbon resin pipe 18 to the electrolytic solutionholding surface 21. The electrolytic solution supply section 28 consistsof a proper fixed displacement pump and a proper solution tank, forexample. Therefore, when an electrolytic solution is supplied from thelower end of the fluorocarbon resin pipe 18 to the electrolytic solutionholding surface 21, the lower faces of the fluorocarbon resin pipe 18and the salt bridge 29 are electrically connected, enabling detection ofthe potential of the electrolytic solution in relation to the referenceelectrode 26. Although a 1M KCl solution is used as the electrolyticsolution in the embodiment, the electrolytic solution should be changedin response to the measurement object. If the measurement object is notwater-soluble, a suitable solvent other than water is selected.

Upon supplying a predetermined amount of electrolytic solution, theelectrolytic solution supply section 28 stops supplying the electrolyticsolution, and is sealed in fluid-sealing relation. The electrolyticsolution is held on the electrolytic solution holding surface 21consisting of the lower faces of the first and second measurementelectrodes 20 and 22 and the two fluorocarbon resin pipes 16 and 18 andthe lower face of the epoxy resin 19 by its surface tension, the surfaceproviding a gas reception portion 23 (i.e., an area directly exposed toa vapor phase).

The silver-silver chloride electrode 24 and the platinum electrodes 12and 14 are connected to a reference electrode input terminal (ref),channel 1 (ch1), and channel 2 (ch2) of an amplifier 30. The amplifier30 compares the potential of the reference electrode 26 with thepotential of the first and second measurement electrodes 20 and 22 andamplifies the voltage difference for supply to a recorder 32. Theamplifier 30 includes a low-noise DC amplifier.

The recorder 32 records the signals supplied from the amplifier 30.Further, a controller 34 controls supplying of an electrolytic solutionby the electrolytic solution reservoir 28 every predetermined time or inresponse to a predetermined operator input. The controller 34 analyzesthe measurement result provided by the recorder 32 and identifies asubstance according to a technique described below.

The vapor phase sensor according to the embodiment has the twomeasurement electrodes 20 and 22 which differ in film composition. Then,a response difference due to the film composition difference can beknown by using the first and second measurement electrodes 20 and 22 forsimultaneous measurement. On actual measurement, the measurement resultof the preferred measurement electrode 20 or 22 can also be used formeasurement.

Measurement Operation!

Detection of chemical substances using the vapor phase sensor describedabove is described with reference to FIG. 3. First, a predeterminedamount of an electrolytic solution is supplied from the electrolyticsolution supply section 28 and is held on the electrolytic solutionholding surface 21 for forming the gas reception portion 23 at step S11.

Next, air containing a stimulant substance is blown against the gasreception portion 23 for a predetermined time at step S12. This step isperformed, for example, as follows: First, 100 μl of a stimulantsolution containing a predetermined chemical substance is measured andis dropped on to a deodorized filter paper 40 (area 5 cm²). The filterpaper 40 is housed in a Pasteur pipette 42 and the rear end of thePasteur pipette 42 is connected via an odorless tube (not shown) to apump (not shown).

In this condition, air is fed from the pump to blow the stimulantsubstance evaporating from the filter paper 40 against the gas receptionportion 23 of the vapor phase sensor. The stimulation time for thestimulant containing gas was 1-20 seconds at a flow velocity of 90ml/min (air velocity 1.9 m/sec). The stimulation time is controlled bythe controller 34 and the flow velocity is monitored with a flow meterand is feedback controlled by the controller 34. A deodorizing tubecontaining activated carbon and a dehydrating tube containing silica gelare located between the pump and the pipette for using air from whichodors and water vapor are removed.

Change with time of the potential difference between the measurementelectrodes 20, 22 and the reference electrode 26 is detected on therecorder at step S13. The detection result is sent to the controller 34,which then analyzes the detection result to identify the chemicalsubstance at step S14. One example of the technique for identifyingchemical substances is given below.

When one measurement terminates in such a manner, whether or not anothermeasurement is to be made is determined at step S15. If it is to bemade, control returns to step S11 at which another electrolytic solutionis supplied. Then, the old electrolytic solution held on theelectrolytic solution holding surface 21 drops as a cleaning solution,and the new electrolytic solution is held on the electrolytic solutionholding surface 21 for updating the gas reception portion 23. Therefore,in the vapor phase sensor, the gas reception portion 23 is updated bythe operation of supplying a new electrolytic solution, enabling thenext measurement to be made easily. In the example, the technique ofblowing air containing a stimulant material against the gas receptionportion 23 was used, but a sampled gas can be blown for detectingchemical substances in the gas. Also, the vapor phase sensor is placedin the atmosphere to be measured and electrolytic solutions arereplaced, thereby measuring chemical substances in the atmospherewhenever necessary.

Experimental Results!

To check the sensor for function, the following were initially used asstimulant solutions for measuring responses:

1. Acid: Acetic acid (stock solution diluted 1 to 10000 times withwater)

2. Alkali: Ammonia (diluted 1000 to 100,000 times with water)

3. Alcohol: Ethanol (stock solution diluted 1 to 100 times with water)

FIG. 4 shows a potential change at the PPy/PVS measurement electrodewhen control (air flow only), ethanol, acetic acid, and ammonia areblown separately for three seconds. Here, the vertical axis indicatesthe potential of the measurement electrode and the horizontal axis thetime. The measurement results of potential change at the firstmeasurement electrode 20 made of PPy/PVS are shown here.

As shown here, for the control, the potential change is small; for theethanol, the potential rises about 2 mV rapidly due to stimulation; forthe acetic acid, the potential rises about 50 mV rapidly due tostimulation; and for the ammonia, the potential falls about 50 mVgradually due to stimulation. Thus, potential changes dependent upon thechemical substances appearing on the first measurement electrode 20.

Then, if the controller 34 previously stores the patterns of thestandard specimens, chemical substances in a vapor phase can bespecified by pattern matching. For composite patterns of a plurality ofsubstances, the chemical substances can be specified if the combinationis moderate.

Further, FIG. 5 shows the relationship between dilution (logarithmicexpression to the base 10) and response amount (indicating the maximumpotential change amount) for acetic acid and ammonia. As shown in thefigure, a given relationship exists between the dilution and responseamount. Chemical substance amount can also be determined by previouslymeasuring calibration curves. Such determination can also be executed bythe controller 34.

Next, the actual measurement results and identification of chemicalsubstances will be described. Two types of substances selected from eachof the ketone class, alcohol class, ester class, amide class, and sulfurcontaining compounds were used as stimulant solutions for detection.Potential responses to the stimulant solutions are shown in FIG. 6.Here, the vertical axis indicates the potential of the measurementelectrode and the horizontal axis the time. The stimulation time wasthree seconds and the first measurement electrode 20 made of PPy/PVS wasused as the measurement electrode.

As shown in FIG. 6, potential responses to all substances were obtained.Moreover, the response pattern varies depending on the substance. Thus,if response patterns to various substances are previously measured, theresponse pattern to the substance being inspected can be compared withthe provided patterns for detecting the chemical substance.

The response patterns changing with time for substances having similarchemical structures (the same class) are similar patterns. Therefore, bymaking an analysis described below, substances can be identified to somedegree; for example, if ethanol is given, it can be identified as asubstance being contained in the alcohol class. That is, the methodaccording to the embodiment enables at least identification of afunctional group of compounds.

Further, if a number of chemical substances are mixed, the chemicalsubstances can be recognized by predetermined pattern recognition.

Thus, according to the chemical substance detecting method in theembodiment, chemical substances in a vapor phase can be identified, sothat odor substances can be identified, for example.

Pattern Analysis!

As described above, odor substances can be identified by comparing thesimilarity of the pattern of the obtained odor substance to those of thepatterns of reference substances previously determined. Such patterncomparison is convenient and easy to determine if it can be quantified.In the embodiment, pattern similarity is quantified routinely accordingto the procedure described below:

<Reference substances and fitting function>

In the embodiment, ethanol, acetone, ethyl acetate, anddimethylformamide were used as reference substances, their patterns ofchange with time were prepared, and factors common to these substanceswere considered for setting the fitting function shown below. Therefore,any pattern of the four substances can be prepared by selecting properparameters of the fitting function (FIG. 7).

Fitting function ##EQU1##

In the embodiment, further, a parameter specified when the fittingfunction is set, which will be hereinafter called the primary parameter,is processed for an analysis to prepare new parameters, called secondaryparameters, and a similarity among the chemical substances is determinedbased on the parameters (FIG. 8). In the embodiment, since the primaryparameter contains factors requiring a relative comparison, they arenormalized to prepare the secondary parameters. In the embodiment, theprimary parameters are stored in a database (see FIG. 8).

<Determination of degree of similarity, using cluster analysis>

In the embodiment, the degree of similarity is determined by conductinga cluster analysis, as described below. Because the number of thesecondary parameters specified in the embodiment is five, a Euclideandistance on the fifth dimension is calculated and is assumed to be theEuclidean Distance. Specifically, the shorter the distance betweenchemical substances, the higher the Euclidean Distance therebetween. Asshown in FIG. 9, according to the analysis, it is found that theEuclidean Distance between ethyl acetate and dimethylformamide is about7 and moreover that they are chemical substances most similar to eachother. Further, the Euclidean Distance of acetone to ethyl acetate ordimethylformamide, whichever is the closer, is about 9. The EuclideanDistance of ethanol to acetone, ethyl acetate, or dimethylformamide,whichever is the closer, is about 11.

In the embodiment, ethyl acetate is selected as a typical substance ofthe ester class, dimethylformamide as a typical substance of the amideclass, acetone as a typical substance of the ketone class, and ethanolas a typical substance of the alcohol class. So long as the results inFIG. 9 are seen, a generalization may be made such that the EuclideanDistance between ester and amide is the shortest and that ester or amideis more similar to ketone than to alcohol. This suggests that chemicalsubstances can be classified according to the type of functional groupthat the chemical substances have.

In the embodiment, the Euclidean distance calculation method is adoptedas the distance calculation method between parameters (measurementmethod), but the calculation method is not limited to this method; inaddition, a squared Euclidean distance, Chebychev distance, or1-correlation coefficient calculation method can also be adopted.

<Identification examples of chemical substances>

Next, an example of identifying substance A to be measured is given withreference to FIG. 10. In the example, 2-heptanone is used as substanceA. When parameters of substance A are calculated and the Euclideandistances between the parameters and the parameters of each referencesubstance (ethanol, acetone, ethyl acetate, and dimethylformamide) arefound, a value of about 2.8 is obtained with respect to acetone andlarger values are obtained with respect to other reference substances.Therefore, it is found that substance A is a compound that is mostsimilar to acetone among the reference substances and moreover thatEuclidean Distance substance A to acetone is about 2.8. This resultshows the fact that substance A is a substance similar to acetone, andsuggests that the chemical group of substance A is likely to be theketone group, as mentioned above. In the example, this estimation iscorrect because substance A is actually 2-heptanone. It can also befound that the Euclidean Distance between the cluster acetone, substanceA! and cluster ethyl acetate, dimethylformamide! is about 9.

Thus, it is also useful to consider the fact for determining thechemical structure of substance A.

If dimethylacetamide is used as substance B in identification example 2(FIG. 11), it is determined that substance B is a substance that is theclosest to dimethylformamide. That is, the parameters of substance B arethe closest to those of dimethylformamide and moreover the Euclideandistance therebetween is about 1.

<Update of database>

The database can be updated. For example, 1-propanol in addition toethanol as an alcohol, 2-heptanone in addition to acetone as a ketone,isoamyl acetate in addition to ethyl acetate as an ester, anddimethylacetamide in addition to dimethylformamide as an amide, can beadded as data. If ethanol and 1-propanol are added as data, in additionto identification of the substance being measured as a probable alcohol,which of ethanol and 1-propanol the substance is close to can also bespecified. For example, if the substance being measured is methanol, itis identified as a substance closer to ethanol than to 1-propanol and if1-butanol is measured, it is identified as a substance closer to1-propanol than to ethanol. Identification of chemical substances can bemade in more detail by adding data for updating the database in such amanner (FIG. 12).

Film Composition Difference and Response Pattern Difference BetweenElectrodes!

FIG. 13 shows response patterns of the two measurement electrodes(PPy/PVS and PPy/Cl) 20 and 22 to the same substances (in this case,2-heptanone and ethanol).

As seen in FIG. 13, the PPy/PVS film responds to 2-heptanone in thepositive direction of potential, but the PPy/Cl film does not show aremarkable response to 2-heptanone. The PPy/PVS film responds to ethanolin the positive direction, but the PPy/Cl film responds to ethanol inthe negative direction.

Thus, different responses to the same chemical substance can be obtainedby changing the type of measurement electrode, namely, the type ofelectrochemically polymerized film. It is considered that the responsedifference reflects the physicochemical property difference betweenelectrochemically polymerized films. Electrochemically polymerized filmsshow physicochemical properties varying depending on ions with which thefilms are doped. Therefore, if response characteristics of more varyingtypes of films are previously examined and a vapor phase sensor providedwith a number of measurement electrodes made of the films is used,accuracy of chemical substance identification can be increased. Further,if a number of chemical substances are mixed, their analysis andidentification are also facilitated.

Response Amounts to Substances!

Not only the response pattern but also the peak potential change amountvaries depending on the substance. Therefore, the peak potential changeamount as well as the response pattern becomes a substanceidentification parameter. In the specification, the potential changeamount at the peak is represented as "response amount."

FIG. 14 shows the response amounts to various substances. Since theresponse amount varies depending on the substance, it can be used todetect a specific chemical substance.

Further, FIG. 15 shows the response amounts to alcohols having differentnumbers of carbon atoms. As shown here, the greater the number of carbonatoms, the smaller the response amount to the alcohol. It is consideredthat solubility in electrolytic solution is reflected. Then, it may bepossible to cover chemical substances having a large number of carbonatoms (or high molecular weight) by changing the composition of anelectrolytic solution. For example, if such a solvent in which ahydrophobic substance dissolves is used, a substance having a largenumber of carbon atoms becomes soluble and therefore may be easilydetected.

FIG. 16 shows the measurement results using 100 μl of a solutioncomprising ethanol diluted with pure water as a stimulant liquid. Thevertical axis indicates the maximum response amounts and the horizontalaxis indicates dilution magnification with logarithms. As understoodfrom the measurement results, the sensor in the embodiment respondssubstantially in direct proportion to the concentration. Therefore, thenature can also be used to determine substances.

Here, the potential change measurement results shown in FIGS. 14-16 areall provided by measurement of the first measurement electrode 20 madeof PPy/PVS.

Preparation of Measurement Electrodes!

Next, preparation of electrochemically polymerized films at themeasurement electrodes 20 and 22 is described with reference to FIG. 17.A desired monomer solution 51 is contained in a vessel 50 and a workingelectrode 52, such as a platinum electrode, for which anelectrochemically polymerized film is to be prepared and a counterelectrode 54 are inserted in the inside of the vessel 50. The workingelectrode 52 is formed like a cylinder and the counter electrode 54 isformed like a hollow cylinder having a part opened surrounding theworking electrode 52. The monomer solution 51 is connected via a saltbridge 57 to a reference electrode 56. The working electrode 52, thecounter electrode 54, and the reference electrode 56 are connected to apower supply 58. A nitrogen gas is introduced into the vessel 50.

To form an electrochemically polymerized film, first the monomersolution 51 is stirred with the nitrogen gas to remove dissolved oxygen.Next, while the working electrode 52 is held at a constant potentialwith respect to the counter electrode 56, a desired current is made toflow from the power supply 58 with the working electrode as a positivepole and the counter electrode as a negative pole for forming anelectrochemically polymerized film 60 on the surface of the workingelectrode 52. Here, a constant potential method, whereby the potentialbetween the working electrode 52 and the counter electrode 54 iscontrolled so that a desired constant potential exists between theworking electrode 52 and the reference electrode 56, or a constantcurrent method, whereby a desired constant current is made to flowbetween the working electrode 52 and the counter electrode 54 so that adesired constant potential exists between the working electrode 52 andthe reference electrode 56, can be used as the voltage applying method.

Thus, the monomer, which is activated by holding the potential of theworking electrode 52 at a predetermined potential, such as 0.6 V, ormore with respect to the reference electrode 56, is deposited on theworking electrode 52 to form a polymer. Since the polymer is conductive,a new polymer is laminated on that polymer if application of potentialis continued, so that the electrochemically polymerized film 60 of athickness matching the applied electricity quantity is formed.

Here, the preparation conditions of the electrochemically polymerizedfilms used in the embodiment are listed:

Monomer solution:

For electrochemically polymerized film PPy/PVS aqueous solution of 0.1Mpyrrole+0.1M polyvinyl potassium sulfate

For electrochemically polymerized film PPy/PVS aqueous solution of 0.1Mpyrrole+0.1M KCl

Electrodes:

Working electrode (+): Platinum disk 1 mm in diameter (area 0.00785 cm²)

Counter electrode (-): Platinum plate

Electrochemically polymerization condition:

Constant current electrolysis 2.5 mA/cm²

Electricity quantity:

For example, films having the following thicknesses can be obtained.When they were used for making an experiment, the thinner films weregood in sensitivity, but stability of measurement potential worsened. Itwas found that film thicknesses 0.25 to 2.5 C/cm² are preferable.

Film thickness 1 (0.25 C/cm², polymerization time 1 min 40 sec)

Film thickness 2 (1.0 C/cm², polymerization time 6 min 40 sec)

Film thickness 3 (2.5 C/cm², polymerization time 16 min 40 sec)

Film thickness 4 (105 C/cm², polymerization time 66 min 40 sec)

Thus, when pyrrole becomes polypyrrole, anions in the monomer solution(PVS- and Cl-) are taken in. Since polaron exist stably in the polymerbecause of the presence of the anions in the polymer matrix, thepolarons function as carriers, thereby making the polymer conductive.The physical property of the electrochemically polymerized film variesdepending on the type of anion.

The following merits are provided by using polypyrrole:

1. Films can be easily formed by electrochemical polymerization;

2. films can be fixed on electrodes as conducting thin films;

3. film thickness can be controlled electrochemically; and

4. replacement of dopants is easy and a proper dopant can be selectedaccording to the measurement object.

Here, thiophene and its derivatives in addition to pyrrole, can be usedas the monomers for forming the electrochemically polymerized films,sodium paratoluenesulfonate (TsONa), quaternary alkyl ammonium nitrate(R4NNO3), etc., in addition to potassium chloride can be used as thesupporting electrolytes, and acetonitrile, propylene carbonate, etc., inaddition to water can be used as the solvents.

As described above, according to the chemical substance detection methodof the invention, chemical substances can be identified from patternsdetected by a single measurement section. Further, measurement can berepeated by updating the electrolytic solution.

Second embodiment!

The vapor phase sensor according to the invention is characterized bythe fact that the surface tension of an electrolytic solution is used tohold the electrolytic solution on the electrolytic solution holdingsurface 21. In the first embodiment, the electrolytic solution isdropped from the holding surface 21 for updating by supplying anotherelectrolytic solution after measurement has been made. In a secondembodiment of the invention, independent means for removing anelectrolytic solution from the holding surface 21 is provided as afeature. Components identical with or similar to those previouslydescribed in the first embodiment are denoted by the same referencenumerals in the description to follow and will not be discussed again.

A vapor phase sensor 60 according to the second embodiment of theinvention has a measurement section 10 mounted on a base 62, as shown inFIG. 18(a). The measurement section 10 comprises first and secondmeasurement electrodes 20 and 22, as in the first embodiment. The vaporphase sensor 60 is provided with a supply pipe 64 and a discharge pipe66, as shown in FIGS. 18(b) and 18(c), which are sectional views of thesensor 60. A reference electrode 26 may be placed in any positionelectrically communicated with the measurement electrodes in anelectrolytic solution; here, the reference electrode 26 (not shown) isdisposed within the supply pipe 64 or the discharge pipe 66. Anelectrolytic solution supplied from the supply pipe 64 is stored in arecess 68 made on the base 62. The electrolytic solution stored in therecess 68 is discharged from the discharge pipe 66. If the electrolyticsolution is supplied with its discharge stopped, a drop 70 is formed onthe recess 68 by its surface tension and the surface of the drop 70forms a gas reception portion 23 as it is. The supply pipe 64 and thedischarge pipe 66 are placed coaxially with each other, as shown in FIG.18(a).

The structure of the vapor phase sensor according to the secondembodiment enables accurate control of the surface area and volume ofthe gas reception portion 23, thus providing the advantage of improvingthe quantitative property of the vapor phase sensor. Also, when theelectrolytic solution is updated, the solution does not scatter to theoutside. Thus, the gas reception portion 23 can be installed in anydirection without being fixed downward as in the sensor according to thefirst embodiment.

To identify a chemical substance in a mixed gas containing a pluralityof chemical substances or to raise the identification accuracy ofchemical substances, a number of sensors having different responsecharacteristics need to be used for measurement. To construct amutisensor consisting of a number of sensors, the structure according tothe second embodiment is also useful. The type of electrochemicallypolymerized film and the type of electrolytic solution are factors forchanging the response characteristics of the vapor phase sensor. Thenumber of electrodes installed in the measurement section 10 can be setfreely in response to the measurement object. The type ofelectrochemically polymerized film can also be changed. Since the supplyand discharge pipes of an electrolytic solution are mounted on the base62 in the second embodiment, a number of vapor phase sensors areconnected to separate supply and discharge channels of electrolyticsolutions, whereby a multisensor can also be provided for changing thetype of electrolytic solution. In fact, if both the film andelectrolytic solution types are optimized in response to the measurementobject, a more effective multisensor can be provided.

Thus, the vapor phase sensor according to the embodiment can detect achemical substance in a vapor phase diffusing into an electrolyticsolution held on the electrolytic solution holding surface 21 as apotential change at the electrodes in the electrolytic solution.

As described above, according to the vapor phase sensor of theinvention, the surface of an electrolytic solution is exposed directlyto the air. Then, odor substance, etc., in a vapor phase can beefficiently diffused into the electrolytic solution; thus, stable andaccurate detection can be made. Particularly, a substance can beaccurately specified by analyzing a change pattern of the electric statedetected (change with time). Further, the electrolytic solution can beeasily updated, so that detection can be executed whenever necessary.Also, high-performance detection can be maintained over a long term bymaking the measurement electrodes of electrochemically polymerizedfilms.

Freshness Measurement of Beef!

<Measurement operation>

An example of detecting the degree of maturity of beef will be describedwith reference to FIG. 19 as one example of a foodstuff freshnessmeasurement method using the vapor phase sensor having theabove-mentioned structure. First, a predetermined amount of anelectrolytic solution is supplied from an electrolytic solutionreservoir 28 and is held on the electrolytic solution holding surface 21for forming the gas reception portion 23 at step S11.

Next, a gas containing odor substances discharged from beef beinginspected is blown against the gas reception portion 23 at step S12.This step is performed, for example, as follows: First, 100 μl ofextracted juice from the beef being inspected is measured and is droppedon deodorized filter paper 40 (area 5 cm²). The filter paper 40 ishoused in a Pasteur pipette 42 and the rear end of the Pasteur pipette42 is connected via an odorless tube (not shown) to a pump (not shown).

In this condition, air is fed from the pump to blow the gas containingodor substances discharged from the beef, evaporating from the filterpaper 40 against the gas reception portion 23 of the vapor phase sensor.The stimulation time for which the gas is blown was 1-20 seconds at flowvelocity 90 ml/min (air velocity 1.9 m/sec). The stimulation time iscontrolled by a controller 34. The flow velocity may be monitored with aflow meter and be feedback controlled by the controller 34. Adeodorizing tube containing activated carbon and a dehydrating tubecontaining silica gel are located between the pump and the pipette forusing air from which odors and water vapor are removed.

The potential difference between the measurement electrodes 20, 22 andthe reference electrode 26 is detected on a recorder at step S13. Thedetection result is sent to the controller 34, which then analyzes thedetection result to calculate the freshness of the beef at step S14. Thedegree of maturity is determined based on the calculation result at stepS15.

To continue subsequent measurement at step S16, a new electrolyticsolution is supplied.

Then, the old electrolytic solution held on the electrolytic solutionholding surface 21 is dropped as a cleaning solution. Thus, the newelectrolytic solution is held on the electrolytic solution holdingsurface 21 for updating the gas reception portion 23. In the example,the technique of soaking the filter paper with the beef juice andblowing air passed through the filter paper against the gas receptionportion 23 was used, but a gas containing odor substances sampled fromthe foodstuff (beef) can be blown for measuring the freshness of thefood. Also, the gas reception portion 23 may be placed in the atmosphereto be measured for measuring at predetermined timing.

<Experimental results>

Next, the actual experiment results will be discussed with reference toFIG. 20. In the experiment, gases containing odor substances dischargedfrom beef samples having different numbers of storage days were measuredas described above. In the experiment, the storage temperature was 23 C.and PPy/PVS films were used on the surface of measurement electrodes.

Under these conditions, each gas was blown against the gas receptionportion 23 for 20 seconds indicated by the solid line in FIG. 20. Asshown here, when the number of storage days is 0, a response in thepositive direction is observed; as the number of storage days increases,a response changes from the positive direction to the negative directionwith a larger response amount, and response patterns also vary. It isconsidered that these reflect the fact that the amounts and types ofchemical substances (odor substances) discharged into the vapor phasefrom the beef vary with the number of storage days.

Therefore, if the features of the response patterns are previouslyextracted, freshness of beef can be calculated by analyzing a responseof the vapor phase sensor, thereby determining the maturity degree.

FIG. 21 shows the relationship between the number of storage days andthe response amount of the sensor. In the figure, "Fresh" denotes notyet tasty (unmatured) beef; "Mature" denotes mature and edible beef; and"Rotten" denotes inedible beef For the response amount, the potentialchange amount at the end of stimulation for 20 seconds was adopted. Theresponse to the fresh beef stored for 0 days is made in the positivedirection, and the response to the mature beef (stored for 0.5, 1 day)is 1. The response to the rotten beef (stored for 1.5 days) is made inthe negative direction.

Therefore, the degree of maturity of beef can be measured by suchmeasurement. Further, the features of response patterns as shown in FIG.20 are extracted, reference values are preset, and the degree ofmaturity is determined based on the patterns, thereby determining itmore accurately.

Freshness of beef can also be measured with the vapor phase sensoraccording to the second embodiment as with the vapor phase sensoraccording to the first embodiment.

As described above, according to the food freshness measurement methodof the invention, chemical substances contained in a vapor phase arediffused into an electrolytic solution and absorbed on the electrodes,causing the electric state of the electrodes to change, and freshness offood is measured in response to the electric state change of theelectrodes. Thus, measurement can be made without human intervention, sothat freshness can be measured objectively. Particularly, it wasdifficult to measure freshness (maturity degree) of beef withconventional measuring instruments, but the invention makes suchmeasurement possible. Preferred beef freshness measurements can be madeby using the electrodes made of conducting polymer films.

Measuring System of Chemical Substances in Vapor Phase!

FIG. 22 is a block diagram showing the configuration of an odormeasuring system as one example of a system of measuring chemicalsubstances in a vapor phase. The odor measuring system 100 ischaracterized by the fact that it comprises a vapor phase sensor 101according to the invention into which the air is led. Either of thevapor phase sensors according to the first and second embodiments can beused for the vapor phase sensor 101. In the odor measuring system 100,the air is sucked in through an air introduction port 103 to introduceit into the vapor phase sensor 101. That is, in the odor measuringsystem 100 according to the embodiment, the vapor phase sensor 101 isattached to the inside of an air introduction pipe 105 for measuringchemical substances contained in the air sucked through the airintroduction port 103, thereby detecting odors. In the embodiment, anair controller 106 is connected to the end of the air suction pipe 105.The air controller 106 comprises an air pump, a flow meter etc., forsucking the air via the air suction pipe 105 from the outside. Asolenoid valve 104 is mounted on the air suction port 103 forcontrolling the on/off operation of air suction and the air suctionamount. In the embodiment, the air suction pipe 105 branches tointroduce cleaning air. A solenoid valve 104 is also mounted on acleaning air introduction port 107, and the cleaning air is controlledby opening and closing the solenoid valve 104. A solution controller 109controls supply and discharge of solutions via the supply pipe 108a anddischarge pipe 108b to and from the vapor phase sensor 101. A signalprocessing display section 110 processes data obtained from the vaporphase sensor 101 and displays the processing result. The signalprocessing display section 110 and the vapor phase sensor 101 areconnected by signal lines 111. The odor measuring system 100 accordingto the embodiment comprises a control section 113, which controls theentire system. The signal processing and display section 110 performsdata processing using the detection method and identification method forchemical substances (as described above) for specifying chemicalsubstances contained in the air. Particularly, if the system is adoptedto detect an odor of beef, it can measure the freshness of beef. Theodor measuring system 100 actively sucks the air and leads it into thevapor phase sensor and therefore can also detect a minute amount of odorsubstance (odor source substance). For example, if the system isinstalled in a refrigerator, rotten foodstuffs stored therein can bedetected easily.

Third embodiment!

<Configuration>

FIG. 23 shows the overall configuration of a system for detectingchemical substances in a liquid phase according to a third embodiment ofthe invention.

FIG. 24 is an enlarged cross-sectional view of a measurement section210.

In this embodiment, the measurement section 210 comprises two platinumelectrodes 120 and 140 and a fluorocarbon resin pipe 160 fixed with anepoxy resin 190. Films made of different conducting polymers areattached to first and second measurement electrodes 200 and 220 providedat lower faces of the platinum electrodes 120 and 140, respectively. Thefirst measurement electrode 200 made of a PPy/PVS (polypyrrole dopedwith polyvinyl sulfite ions) film, for example, is formed on the lowerface of the platinum electrode 120, and the second measurement electrode220 made of a PPy/Cl (polypyrrole doped with chloride ions) film, forexample, is formed on the lower face of the platinum electrode 140. Theplatinum electrodes 120 and 140 may have the lower ends only formed withplatinum disks. The conducting polymer films are formed byelectrochemical polymerization or chemical polymerization in a mannersimilar to that mentioned in the preparation of measurement electrodesin the first embodiment.

The fluorocarbon resin pipe 160 includes a salt bridge 290 made of 3M(mol/l) KCl (potassium chloride) and 3% agar. A silver chlorideelectrode 240 is fitted to an upper end of the salt bridge 290, forminga reference electrode 260. Generally, the entire solution containing thesilver-silver chloride electrode 240 and chloride ions is called thereference electrode, but the lower end of the salt bridge 290 is calledthe reference electrode 260 in this embodiment for the description ofthe operation, etc., because they are substantially the same. Themeasurement section 210 may have a counter electrode (not shown) that isindependent from the reference electrode 260. The system also providestwo kinds of solution supply sections 280 and 281 which are connected tothe measurement section 210 by a solution guide 286. One of these is anelectrolytic solution supply section 280 including a storage 282 and apump 283 for supplying an electrolytic solution to the measurementsection 210 to stabilize a potential of the electrodes. The other is asample solution supply section 281 including a storage 284 and a pump285 for supplying a sample solution to the measurement section 210. Theflow of each solution from the electrolytic solution supply section 280and the sample solution supply section 281 can be controlled by a valve287 which is provided on the solution guide 286. The valve can be openedat a predetermined interval or in response to an input by an operator.

The silver-silver chloride electrode 240 and the platinum electrodes 120and 140 are connected to a reference electrode input terminal (ref),channel 1 (ch1), and channel 2 (ch2) of an amplifier 300. The amplifier300 compares the potential of the reference electrode 260 with thepotential of the first and second measurement electrodes 200 and 220 andamplifies the difference voltage for supply to a recorder 320. Theamplifier 300 includes a low-noise DC amplifier.

The recorder 320 records the signals supplied from the amplifier 300.The measurement result provided by the recorder 320 is provided to acomputer (not shown) which analyzes and identifies a substance accordingto the technique described in the pattern analysis of the firstembodiment.

The liquid phase sensor according to this embodiment has two measurementelectrodes 200 and 220 which differ in film composition. The twomeasurement electrodes 200 and 220 are prepared in a similar manner asthe first embodiment. Then, a response difference due to the filmcomposition difference can be determined by using the first and secondmeasurement electrodes 200 and 220 for simultaneous measurement.

<Measurement operation>

Detection of chemical substances using the system described above isdescribed with reference to FIG. 25.

First, an electrolytic solution is supplied from the electrolyticsolution supply section 280 to the measurement section 210 through thevalve 287 and is held at the measurement section 210 for stabilizing apotential of the electrodes at step S110.

Next, a sample solution containing a chemical substance is supplied tothe measurement section 210 from the sample solution supply section 281through the valve 287 for a predetermined time. The sample solutionreplaces the electrolytic solution, which has been introduced to themeasurement section 210 at step S120. In accordance with preferredembodiments, the sample solution is held at the measurement section 210or flown at a predetermined rate. The sample solution may be diffusedinto the electrolytic solution with a predetermined concentration ratio.

Changes with time in the potential difference between the measurementelectrodes 200, 220 and the reference electrode 260 are detected on therecorder at step S130. The detection result is sent to the computer (notshown), which then analyzes the detection result to identify thechemical substance at step S140. In this embodiment, a technique foridentifying chemical substances similar to the first embodiment is used.

When one measurement is completed in the manner described above, adetermination is made as to whether or not another measurement is to bemade at step S150. If it is to be made, the control proceeds to stepS160 and returns to S110 at which another electrolytic solution issupplied for cleaning and stabilizing the surfaces of the electrodes.Therefore, in the liquid phase sensor, the measurement section 210 isrefreshed by the operation of supplying a new electrolytic solution. Asa result, it is ready for the next measurement.

<Measuring system of chemical substances in liquid phase>

FIG. 26 is a block diagram showing the configuration of a measuringsystem 500 for measuring chemical substances in various liquid phases asone embodiment of the present invention. The measuring system 500includes a liquid phase sensor 501 into which a solution is led. Theliquid phase sensor described above can be used for the liquid phasesensor 501. In the measuring system 500, the solution is sent through asolution introduction port 503 to the liquid phase sensor 501. Accordingto this embodiment, the liquid phase sensor 501 is attached to theinside of a solution introduction pipe 505 for measuring chemicalsubstances contained in the solution sent through the solutionintroduction port 503. In this embodiment, a solution controller 506 isconnected to the end of the solution introduction pipe 505. The solutioncontroller 506 includes a liquid pump, a flow meter etc., for sendingthe solution via the solution introduction pipe 505 from the outside. Asolenoid valve 504 is mounted on the solution introduction port 503 forcontrolling the on/off operation of solution flow and the solutionamount. In this embodiment, the solution introduction pipe 505 branchesto introduce cleaning solution. A solenoid valve 504 is also mounted ona cleaning solution introduction port 507, and the cleaning solution iscontrolled by opening and closing the solenoid valve 504.

A signal processing/display section 510 processes data obtained from theliquid phase sensor 501 and displays the processing result. The signalprocessing/display section 510 and the liquid phase sensor 501 areconnected by signal lines 511. The measuring system 500 according to theembodiment includes a control section 513, which controls the entiresystem. The signal processing/display section 510 performs dataprocessing using the detection method and identification method forchemical substances as described in the first embodiment for specifyingchemical substances contained in the sample solution.

FIG. 27 shows a structure of a solution supply system 600 for supplyingvarious liquid phases that can be used with the measuring system ofchemical substances described above. The solution supply system 600includes plural solution pipes and valves, for example 504a, 504b and504c, which are used for independently detecting plural sample solutionsA, B and C without mixing the sample solutions with one another.

However, in an alternative embodiment, the solution supply system 600may be used to mix a sample solution and an electrolytic solution at apredetermined concentration ratio.

In another embodiment, the sample solution or the mixture of the samplesolution and an electrolytic solution may be injected into the solutionintroduction pipe 505 by a syringe in a manner similar to the gas orliquid chromatography technique.

What is claimed is:
 1. A method of detecting a chemical substance in aliquid phase comprising the steps of:(a) contacting a liquid phasecontaining a chemical substance to an electrode; and (b) detectingchanges in an electric state at the electrode over time caused by thediffusion and absorption of said chemical substance on said electrode,wherein said chemical substance in said liquid phase is detected basedon the detected change of the electric state over time.
 2. The method ofclaim 1, the method further including detecting the chemical substancebased upon a comparison of a set response pattern to a time varyingelectric state at the electrode.
 3. The method of claim 1, the methodfurther including detecting the chemical substance based upon comparisonof a previously obtained response patterns to a time varying electricstate at the electrode.
 4. The method of claim 1, the method furtherincluding:diffusing a sample of the chemical substance into anelectrolytic solution having a set concentration ratio; and detectingchanges in the electric state at the electrode over time resulting fromthe diffusion of said chemical substance into the electrolytic solution.5. The method of claim 1, the method further including contacting aliquid phase containing a mixture of a sample of the chemical substanceand an electrolytic solution at a set concentration ratio.
 6. A methodof detecting a chemical substance in a liquid phase comprising the stepsof:(a) supplying an electrolytic solution to be in contact with aplurality of electrodes for stabilizing an electric state at saidelectrodes; (b) diffusing a chemical substance in a sample solution intosaid electrolytic solution; and (c) detecting changes in the electricstate at said electrodes in contact with said electrolytic solution overtime, the changes being caused by diffusion and absorption of saidchemical substance on said electrodes, wherein said chemical substancein said sample solution is detected based on the detected changes of theelectric state over time.
 7. The method of claim 6, the method furtherincluding detecting the chemical substance based upon a comparison of aset response pattern to a time varying electric state at the electrodes.8. The method of claim 6, the method further including detecting thechemical substance based upon comparison of a previously obtainedresponse patterns to a time varying electric state at the electrode. 9.The method of claim 6, the method further including:diffusing a sampleof the chemical substance into an electrolytic solution at a setconcentration ratio; and detecting changes in the electric state at theelectrodes over time resulting from the diffusion of said chemicalsubstance into the electrolytic solution.
 10. A method of detecting achemical substance in a liquid phase comprising the steps of:(a)supplying an electrolytic solution to be in contact with a plurality ofelectrodes and for stabilizing electric states at said electrodes; (b)displacing said electrolytic solution with a sample solution including achemical substance; and (c) detecting changes in the electric states atsaid electrodes over time caused by diffusion and absorption of thechemical substance on said electrodes, wherein said chemical substancein said sample solution is detected based on the detected changes overtime.
 11. The method according to claim 10, wherein after said step ofdetecting changes in electric states, an electrolytic solution issupplied from an electrolytic solution reservoir for replacing saidsample solution with a fresh electrolytic solution to prepare fordetecting a further substance in sample solution.
 12. The method ofclaim 10, the method further including detecting the chemical substancebased upon a comparison of a set response pattern to a time varyingelectric state at the electrodes.
 13. The method of claim 10, the methodfurther including detecting the chemical substance based upon acomparison of previously obtained response patterns to a time varyingelectric state at the electrodes.
 14. The method of claim 10, the methodfurther including:diffusing a sample of the chemical substance into anelectrolytic solution at a set concentration ratio; and detectingchanges in the electric states at the electrodes over time resultingfrom the diffusion of said chemical substance into the electrolyticsolution.
 15. A method of identifying a chemical substance contained invarious phases comprising the steps of:(A) obtaining a fitting functionand parameters associated with a chemical substance selected as areference substance, said step including the steps of:(a1) diffusing thechemical substance selected as the reference substance into the phasesurrounding electrodes; (a2) detecting changes in the electric states atsaid electrodes existing in said phase over time caused by diffusion andabsorption of the chemical substance on said electrodes and preparing apattern of the changes in the electric states over time; and (a3)setting a fitting function based on the pattern and finding parametersof the reference substance for the fitting function; (B) obtainingparameters from a chemical substance being measured, said step includingthe steps of: (b1) diffusing the chemical substance being measured intothe phase surrounding the electrodes; and (b2) detecting changes inelectric states at said electrodes existing in said phase over timecaused by diffusion and absorption of the chemical substance on saidelectrodes and preparing parameters of the substance being measured forthe fitting function; and (C) comparing the parameters of the referencesubstance and the parameters of the substance being measured tocorrelate the reference substance with the substance being measured,wherein said phase includes a phase selected from the group consistingof a liquid phase and a vapor phase.
 16. A method of identifying achemical substance contained in a liquid phase comprising the stepsof:(A) supplying an electrolytic solution about a plurality ofelectrodes to stabilize an electric state at said electrodes; (B)obtaining a fitting function and parameters from a chemical substanceselected as a reference substance, said step including the steps of:(b1)replacing said electrolytic solution with a reference solution includinga chemical substance selected as the reference substance to stabilizesaid electric state at said electrodes; (b2) detecting changes in saidelectric states at said electrodes existing in said electrolyticsolution and said reference solution over time, the changes being causedby diffusion and absorption of the chemical substance on saidelectrodes, and preparing a pattern of the changes in the electricstates over time; and (b3) setting a fitting function based on thepattern and identifying parameters of the reference substance for thefitting function; (C) obtaining parameters from a chemical substancebeing measured, said step including the steps of:(c1) displacing saidelectrolytic solution or said reference solution with a sample solutionincluding the chemical being measured to stabilize said electric statesat said electrodes; and (c2) detecting changes in electric states atsaid electrodes existing in said electrolytic solution and saidreference solution over time, the changes being caused by diffusion andabsorption of the chemical substance on said electrodes, and preparingparameters of the substance being measured for the fitting function; and(D) comparing the parameters of the reference substance and theparameters of the substance being measured to correlate the referencesubstance with the substance being measured.
 17. A liquid phase sensorcomprising:(A) a measurement electrode; (B) a reference electrode; (C) ameasurement section containing at least said measurement electrode andsaid reference electrode for contacting a replaceable solution onsurfaces of said measurement electrode and said reference electrode; (D)a source for supplying an electrolytic solution to said measurementsection; (E) a sample source for supplying a sample solution containinga chemical substance to said measurement section; and (F) am analysissection for detecting a change in an electric state over time betweensaid measurement electrode and said reference electrode caused bydisplacement of said electrolytic solution with said sample solution.18. The liquid phase sensor as claimed in claim 17, wherein the samplesolution contacting said measurement section is replaced with a freshelectrolytic solution from said source for supplying the electrolyticsolution for detecting a substance in a sample solution.
 19. The liquidphase sensor as claimed in claim 17, wherein a surface of saidmeasurement electrode comprises a conducting polymer.
 20. The liquidphase sensor as claimed in claim 17, wherein the sample source comprisesplural sample solution reservoirs and valves for separation of eachsample solution.
 21. The liquid phase sensor of claim 17, wherein thesource for supplying the electrolytic solution supplies the electrolyticsolution at a set concentration ratio and the measurement sectionpermits diffusion of sample solution into the electrolytic solution.